`MSC:15`

`2/5=(2xx3)/(5xx3)= 6/15`

`7/15` giữ nguyên

__

`MSC : 24`

`3/4=(3xx6)/(4xx6)= 18/24`

`5/6 =(5xx4)/(6xx4)= 20/24`

__ 

`MSC : 99`

`8/9 =(8xx11)/(9xx11)= 88/99`

`8/11=(8xx9)/(11xx9)= 72/99`

__

`MSC:30`

`1/2 =(1xx15)/(2xx15)= 15/30`

`2/3=(2xx10)/(3xx10)=20/30`

`3/5=(3xx6)/(5xx6)= 18/30`

\(a,\)\(\dfrac{2}{5};\dfrac{7}{15}\left(MSC:15\right)\)

\(\dfrac{2}{5}=\dfrac{2\times3}{5\times3}=\dfrac{6}{15}\)

\(b,\dfrac{3}{4};\dfrac{5}{6}\left(MSC:12\right)\)

\(\dfrac{3}{4}=\dfrac{3\times3}{4\times3}=\dfrac{9}{12}\)

\(\dfrac{5}{6}=\dfrac{5\times2}{6\times2}=\dfrac{10}{12}\)

\(c,\dfrac{8}{9};\dfrac{8}{11}\left(MSC:99\right)\)

\(\dfrac{8}{9}=\dfrac{8\times11}{9\times11}=\dfrac{88}{99}\)

\(\dfrac{8}{11}=\dfrac{8\times9}{11\times9}=\dfrac{72}{99}\)

\(d,\dfrac{1}{2};\dfrac{2}{3};\dfrac{3}{5}\left(MSC:30\right)\)

\(\dfrac{1}{2}=\dfrac{1\times15}{2\times15}=\dfrac{15}{30}\)

\(\dfrac{2}{3}=\dfrac{2\times10}{3\times10}=\dfrac{20}{30}\)

\(\dfrac{3}{5}=\dfrac{3\times6}{5\times6}=\dfrac{18}{30}\)

1. a) Ta có BCNN(12, 15) = 60 nên ta lấy mẫu chung của hai phân số là 60. 

Thừa số phụ:

60:12 =5; 60:15=4

Ta được:

\(\frac{5}{{12}} = \frac{{5.5}}{{12.5}} = \frac{{25}}{{60}}\)

\(\frac{7}{{15}} = \frac{{7.4}}{{15.4}} = \frac{{28}}{{60}}\)

 b) Ta có BCNN(7, 9, 12) = 252 nên ta lấy mẫu chung của ba phân số là 252. 

Thừa số phụ:

252:7 = 36; 252:9 = 28; 252:12 = 21

Ta được:

\(\frac{2}{7} = \frac{{2.36}}{{7.36}} = \frac{{72}}{{252}}\)

\(\frac{4}{9} = \frac{{4.28}}{{9.28}} = \frac{{112}}{{252}}\)

\(\frac{7}{{12}} = \frac{{7.21}}{{12.21}} = \frac{{147}}{{252}}\)

2. a) Ta có BCNN(8, 24) = 24 nên:

\(\frac{3}{8} + \frac{5}{{24}} = \frac{{3.3}}{{8.3}} + \frac{5}{{24}} = \frac{9}{{24}} + \frac{5}{{24}} = \frac{{14}}{{24}} = \frac{7}{{12}}\)

 b) Ta có BCNN(12, 16) = 48 nên:

\(\frac{7}{{16}} - \frac{5}{{12}} = \frac{{7.3}}{{16.3}} - \frac{{5.4}}{{12.4}} = \frac{{21}}{{48}} - \frac{{20}}{{48}} = \frac{1}{{48}}\).

a)1/2=6/12;2/3=8/12;5/6=10/12;giữ nguyên phan số 7/12

b)5/6=60/72;4/9=32/72;7/24=21/72

c)3/4=45/60;5/12=25/60;2/3=40/60;7/15=28/60

mk trước bạn Nguyễn Ngọc Quý

a: 5/6=25/30

9/30=9/30

b: 7/8=49/56

5/7=40/56

c: 2/9=4/18

5/18=5/18

d: 3/10=6/20

1/4=5/20

 5/6=25/30

9/30=9/30 

7/8=49/56

5/7=40/56

 2/9=4/18

5/18=5/18

 3/10=6/20

1/4=5/20

\(a)\) Mẫu số chung: 45.

\(\dfrac{2}{5}=\dfrac{2\times7}{5\times7}=\dfrac{14}{45}\\ \dfrac{13}{15}=\dfrac{13\times3}{15\times3}=\dfrac{39}{45}\\ \dfrac{19}{45}\)

b) Mẫu số chung: 16.

\(\dfrac{1}{2}=\dfrac{1\times8}{2\times8}=\dfrac{8}{16}\\ \dfrac{3}{8}=\dfrac{3\times2}{8\times2}=\dfrac{6}{16}\\ \dfrac{5}{4}=\dfrac{5\times4}{4\times4}=\dfrac{\dfrac{20}{16}\\ 7}{16}\)

A) 63/90 và 80/90

B) 180/105 và 63/105

7\10=7 nhân 9 và 10 nhân 9=63/90

8/9=8 nhân 10 và 9 nhân 10=8o/90

b12/7=12 nhân 15 và 7 nhân 15=225 và 105

9/15=9 nhân 15 và 7 nhân 7 =63 /105

Bài 1:

a) 

\(\dfrac{1}{2}=\dfrac{1\times6}{2\times6}=\dfrac{6}{12}\)

\(\dfrac{2}{3}=\dfrac{2\times4}{3\times4}=\dfrac{8}{12}\)

\(\dfrac{3}{4}=\dfrac{3\times3}{4\times3}=\dfrac{9}{12}\)

b)

\(\dfrac{1}{3}=\dfrac{1\times15}{3\times15}=\dfrac{15}{45}\)

\(\dfrac{2}{15}=\dfrac{2\times3}{15\times3}=\dfrac{6}{45}\)

\(\dfrac{4}{45}\) (giữ nguyên)

c)

\(\dfrac{1}{8}=\dfrac{1\times3}{8\times3}=\dfrac{3}{24}\)

\(\dfrac{2}{3}=\dfrac{2\times8}{3\times8}=\dfrac{16}{24}\)

\(\dfrac{5}{2}=\dfrac{5\times12}{2\times12}=\dfrac{60}{24}\)

d)

\(\dfrac{2}{7}=\dfrac{2\times4}{7\times4}=\dfrac{8}{28}\)

\(\dfrac{9}{4}=\dfrac{9\times7}{4\times7}=\dfrac{63}{28}\)

\(\dfrac{5}{28}\) (giữ nguyên)

Bài 2:

a)

\(4=\dfrac{4}{1}=\dfrac{4\times12}{1\times12}=\dfrac{48}{12}\)

\(\dfrac{9}{4}=\dfrac{9\times3}{4\times3}=\dfrac{27}{12}\)

b)

\(\dfrac{5}{8}=\dfrac{5\times30}{8\times30}=\dfrac{150}{240}\)

\(\dfrac{25}{30}=\dfrac{5}{6}=\dfrac{5\times40}{6\times40}=\dfrac{200}{240}\)

\(2=\dfrac{2}{1}=\dfrac{2\times240}{1\times240}=\dfrac{480}{240}\).

giúp mình với ạ!